Andrew Harrer/Bloomberg via Getty Images(WASHINGTON) -- The United States is stepping up its missile defenses in Alaska, a response to new threats from North Korea.

The Pentagon plans a nearly 50 percent increase in the number of ground-based missile interceptors on the West Coast -- from 30 to 44. Defense Secretary Chuck Hagel says it's meant to "stay ahead of the threat" posed by Iran and North Korea.

But while Hagel acknowledges the systems haven't always worked in testing, “the American people should be assured that our interceptors are effective,” he said.

“Clearly the United States is sending a strong signal to North Korea that we see your threats,” ABC News military consultant Steve Ganyard.

Defense officials say North Korea's missile program is "maturing," with mobile systems that may be capable of reaching the U.S.